Flexing your bandwidth

Increasing bandwidth demands from the roll-out of new services, coupled with falling costs of optical components and fiber cable, are forcing broadband network operators to once again review the way they're designing their networks. More often than not, they're becoming increasingly interested in reducing node sizes-sometimes to a level considered economically impossible just a few short years ago.

Led by AT&T Broadband and Internet Service's much-documented LightWire architecture that's currently being built and tested in Utah, other large cable operators are keeping a close eye on technological developments that are pushing optics to the curb, and in some cases, all the way to the house.

The demand for more bandwidth, highly reliable networks and a reduction in maintenance costs is also resulting in an increase in the number of vendors entering the marketplace in search of new customers. Some that have cut their teeth with the Regional Bell Operating Companies are now knocking on cable operators' doors as well.

Marconi Communications demonstrated its new "Deep Fiber HFC" architecture at December's Western Cable Show. Based on Marconi's successful, telco-centric DISC*S access platform, this new architecture has been tailored specifically to cable MSOs that want to integrate voice, data and video over a single network.

Figure 1: Optical SolutionsÕ fiber-to-the-home architecture

"Cable operators are pursuing additional revenue from telephony and data services and are seeking to bundle those services," says Tom Spoor, a cable veteran who is now a product line manager at Marconi.

Currently being trialed by at least two unspecified cable operators, the Deep Fiber platform utilizes fiber-to-the-curb concepts and marries them to familiar cable TV concepts and hardware, including coaxial drops, cable modems and set-top boxes in the home.

The system incorporates a host digital terminal (HDT) and an optical network unit (ONU) in the field. Each HDT can serve up to 84 ONUs, which, in turn, can connect with eight to 32 subscribers each.

Telephone voice services are transported via a Sonet ring and delivered to the HDT, which is located in the headend or in a neighborhood. Using a single fiber from the HDT to the ONU, voice traffic is sent over 1310 nm optics, then converted to 24 lines of analog POTS at the ONU.

Video and data are sent from the headend to the HDT over 1550 nm optics. At the HDT, the stream is split and sent to the ONUs. At the HDT, the POTS traffic is combined with the video and data signals on a single fiber using wave division multiplexing, while at the ONU, those services are separated, converted to electrical signals and sent over coax to the home.

In the upstream direction, RF signals are sent to a splitter in the ONU, where they are combined with other upstream information and sent back to the HDT. Upstream RF return and POTS signals are handled separately from the downstream traffic within the HDT.

To power the network, a single 22-gauge twisted pair wire runs from the HDT to the ONU.

Why is the voice traffic not part of the RF mix? Because cable operators looking to provide telephony services are focused on providing carrier-class, lifeline service, says Spoor, who says he's expecting to engage in field trials with nearly every major MSO. He adds that cable operators like this approach because it delivers video and data using technology that field techs and installers are familiar with, yet exposes them to telephony technology.

"The MSOs are all interested in trials right now because they want to know their techs can learn the technology and step up" to maintain and troubleshoot the system, says Spoor.

Marconi, which recently acquired and integrated Reltec and Fore Systems into its business, also recently announced that its ATM-based DISC*S product would be used by BellSouth in its integrated services deployment. BellSouth has already installed Marconi's first-generation hardware, which is serving roughly 500,000 homes in the Southeast.

Also poised to capitalize on the new economics of fiber-rich networks is Optical Solutions, which touts its fiber-to-the-home system as a way for service providers to offer bundled services over a true passive optical network.

The system uses two fibers (one for upstream and one for downstream traffic), and delivers up to six telephone lines, up to 135 analog or digital video channels and high-speed data in 64-kilobit-per-second increments to the home-mounted universal demarcation point (UDP), according to Dave Reiber, western sales manager for the company.

Because it uses RF transmission methods, all services are compatible with existing customer premise equipment, including telephones, televisions and cable modems. In the upstream, video is sent in the traditional 5 MHz to 40 MHz band, while voice and data are sent back between 150 MHz and 300 MHz.

To date, at least 10 network operators have committed to use the FiberPath technology, and four have been publicly announced: Rye Telephone Co. in Colorado; All West Communications in Utah; Futureway Communications in Canada; and the Blair Telephone Co. in Nebraska.

Rye, a company that serves 2,300 lines near Pueblo, Colo., is using the system to serve roughly 650 large-acreage lots. So far, service is being provided to 18 new homes, each of which has an average drop length of 2,200 feet. With drop lengths like that, Rye engineers decided it was more practical to use fiber than copper to provide broadband services to customers.

Futureway in Canada opted to use the Optical Solutions PON architecture because its passive nature doesn't require above-ground pedestals and other cabinets that people are increasingly viewing as eyesores. The system is being installed in a new, urban housing development that is focused on offering its residents a clean, uncluttered landscape.

Figure 2: Marconi's DISC*S Deep Fiber HFC approach.

Futureway, a certified CLEC, plans to serve up to 20,000 premises with the system and is already installing equipment to serve 5,000 homes. System engineers chose FiberPath because increasing bandwidth consumption by local residents threatened to make any newbuild based on HFC or traditional telco architectures obsolete almost before it was finished.

Blair Telephone is using a derivative of FiberPath that it calls "fiber near the home" in a new housing development near Blair, Neb. In this scenario, Blair will upgrade the network to true FTTH when more homes are built and occupied. HunTel Engineering, which owns Blair Telephone, also owns TelePartners, the local cable TV company. Company officials liked the FiberPath system because it was compatible with analog TV, interfaced well with cable modems and provided a telephony solution.

Reiber says that FiberPath is particularly attractive to independent telcos and other carriers who are building in greenfield areas that can tap into multiple revenue streams. Some existing cable companies are also interested because with a passive, all-fiber plant, there's no upstream signal degradation or noise generation, which significantly reduces operational and maintenance headaches, says Reiber.

Adding fuel to the fiber-to-the-home notion is longtime cable TV supplier Ortel Corp., which displayed a prototype FTTH receiver module at the Western Show. The "overlay" receiver delivers up to 110 cable TV channels and 192 DBS channels and provides enough RF gain to drive multiple TVs via 200 feet of in-home coaxial cable. The unit can be powered via an electrical panel or an in-home AC outlet.

Although Ortel showed it's ready for the migration of fiber to the home, internal debate still rages as to when that eventuality will-or should-occur.

Ortel's FTTH receiver prototype.

"I don't want to wreck my career on the rocks of fiber-to-the-home or fiber-to-the-curb, but it's no more expensive in greenfield applications to bring fiber to the curb or to the home than it is to bring copper," says Jeff Rittichier, vice president of marketing at Ortel.

To some degree, cable MSOs are being pushed to deploy fiber deeper by increasing competitive threats, notes Rittichier.

With the RBOCs upgrading five percent of their plants every year, and growing the size of their networks by five percent in newbuilds, Rittichier says that fiber could penetrate deeply into the access network in a relatively short amount of time.

Rittichier

In response, cable operators will keep a close eye on AT&T's LightWire project, and probably develop hybrid architectures that take advantage of more fiber, yet are less costly than true FTTH approaches.

"I think it'll be a case of gradual migration to 60 homes per node over the next three to five years," predicts Rittichier.

"It's a matter of when, not if, for fiber-to-the-home," says Ron Hartmayer, marketing director for broadband communications at Ortel. Noting that there are already numerous trials and demand created by network service providers wishing to add new services, Hartmayer says he sees FTTH becoming commonplace within the next five years.

That sets up an interesting-and daunting-situation for small cable operators who are already struggling to stay in lockstep with the nation's largest MSOs, and a step ahead of the competition. Cash-strapped already, those operators will soon be faced with only a few options: sell their properties to larger operators or partner with a complementary service provider.

For more conventional architectures, Ortel recently developed a new laser and a new photodiode to help network operators deploy networks with higher performance levels, but lower distortion.

The new Mercury Laser 1310 nm module offers a 31 milliwatt output power figure and can operate within spec over a -40 degree C to 85 degree C temperature range, according to Rittichier. Using this laser, network designers can either send signals over a longer path or support a greater number of optical splits.

The company's new photodiode offers high linearity and low capacitance over a 1 GHz bandwidth and is housed in a small, ruggedized coaxial package, Rittichier says. The photodiodes can be used in optical receivers that support analog cable TV, digital video, passive optical networks, fiber-to-the-curb and fiber-to-the-home applications.

Despite the fact that most major cable operators are taking a prudent approach to node size reduction, waiting for increased revenues to force such reductions, technologists are keenly aware of fiber's new economics and the work that's being done to drive fiber connections close to home. The relentless consumption of bandwidth by residents-and, increasingly, businesses-will keep network engineers busy for some time to come.